Traditionally, vaccination against pathogenic human viruses has utilized either live attenuated preparations, whole killed virus or recombinant proteins. Of these approaches, only live attenuated virus preparations activate all arms of the immune system in a manner similar to native infection. Genetic immunization is dependent upon injection of a nucleic acid sequence directly into a host target tissue. In theory, direct genetic immunization should mimic aspects of attenuated vaccines in that synthesis of specific foreign proteins would be accomplished in the host and become the subject of immune surveillance via both the MHC class I and class II pathways. The use of this new technology to immunize animals with a human immunodeficiency virus type 1 (HIV-1) envelope gp 160 DNA construct and achieve relevant immune responses has been reported by this group. Antisera from genetically immunized animals including, mice, rabbits and non-human primates, demonstrate anti-HIV envelope glycoprotein immune responses. The antiserum neutralizes HIV-1 infection and inhibits cell to cell infection in vitro. This technology induced both T cell proliferation and isotype switching consistent with the production of relevant T helper immune responses. Furthermore it was demonstrated that CTL lysis of relevant env expressing targets was similarly induced. Through the development of an in vivo murine model we demonstrated that mice can reject lethal cell challenge through specific immune responses directed at HIV proteins. This in vivo anti HIV data suggest the utility of this specific immune responses elicited by intramuscular injection of genes. While all arms of the immune system are elicited by genetic immunization, the fine specificity of the responses induced have not been characterized in detail. More importantly, the ability of this strategy to induce protective responses in humans and non-human primates has yet to be established. This proposal will focus on the analysis of this approach to effectively induce such protective immunity from lentiviral challenge. The overall strategy will be to perform in depth analysis of specific immune responses against SIV constructs in mice, which will aid our studies in non-human primates. Constructs will be developed for expression of the SIV239 env and gag/pol genes and evaluated in vitro for expression in relevant cell lines. These will then be analyzed in preliminary inoculation studies in mice, their in vivo immunogenicity will be analyzed. These results will give insight into the experiments in non- human primates where similar analysis of the immune responses generated by construct inoculation will be performed. Finally the SIV constructs will be analyzed for their protective potential in vivo in viral challenge experiments. Together these studies will characterize the potential of this new technology for the development of facilitated genetic inoculation protocols as a potential prophylactic vaccine or against pathogenic primate lentiviruses. These studies have direct relevance to vaccine development against HIV-1.